Gerwyn, you make a good point about HERV replication and I just realized I may have addressed the wrong point above. Were you talking about the culture study? If so, consider that the amplification process used by WPI might have amplified HERVs if the proteins they used were part of the triggering mechanism for those HERVs. And how interesting that they amplified the suspected XMRV in a prostate cancer cell line, a cell line that is already known to express the target antigens! That increases the chance of a HERV activation in my opinion. However it still is a stretch of an explanation for a false positive, I would agree with that. But go back to my comments about researcher bias, if a researcher is trying to build a case for something, they hunt and hunt until they find a reaction, and in that process sometimes they simply discover a new false positive mechanism.